Vertebroplasty, or kyphoplasty, is a treatment used in patients with vertebral compression fractures.
Many causes can determine the collapse of a vertebra under the action of the compressive forces that normally affect the spinal column: painful compression fractures from osteoporotic, traumatic or osteolytic compression of the thoracic or lumbar vertebrae can occur. The main causes are osteoporosis, multiple myeloma, vertebral metastases, or more simply a trauma.
As is known (see accompanying FIGS. 1 and 2), the vertebrae 10 have a main body 11 of a substantially cylindrical shape (or better, slightly “hourglass” shape), in which a peripheral ring of cortical bone and a central portion of cancellous bone 12 and a plurality of processes (superior articular, inferior articular, transverse and spinous) that extend posteriorly 13 are identifiable.
80% of the load is borne by the main body 11, while the pedicles and the processes 13 perform a dynamic function and are allocated to bear only a small portion of the load.
Compression fractures therefore substantially concern the main body.
As mentioned, the fracture can originate due to an osteoporosis situation affecting the cancellous bone, which, due to the compromised trabecular structure, no longer exerts its support function and collapses under the action of compression loads. A collapse of the cancellous bone then involves the occurrence of fractures even in the cortical bone.
Surgical methods are known in the prior art that are aimed at restoring the load-bearing capacity of the vertebra by means of the insertion of prosthetic aids such as flexible rods, screws and nails.
These surgeries, as can also be understood by those not skilled in the art, are very invasive both due to the fact that they require the surgeon to create a large access means, and due to the fact that the application of rods, screws and nails is in any case an surgery that is heavy for the patient's body and burdensome from the point of view of the body's full adaptation in the presence of the prosthesis.
A mini-invasive surgical technique has been more recently developed and established that requires both a much more contained access means, of a few millimeters, and reduced stress for the patient's body, even in the post-surgical period.
This technique is known as kyphoplasty or vertebroplasty, and is performed by inserting a balloon catheter or a mechanical dilator made of polymer material into the vertebral body through a metal cannula of a greater size (about 5 mm in diameter).
The technique most used provides for the use of a balloon 30: the surgeon, after creating the necessary access means, inserts the cannula 20 into the collapsed vertebra, which allows the balloon 30 to be inserted into the main body 11 of the vertebra, in the area in which the collapsed cancellous bone 12 no longer performs its support function.
With the patient in the prone and distracted position, one proceeds with the insertion of the cannula directly into the main body of the vertebra, with transpedicular access. The entire surgical step takes place under fluoroscopy.
Once the correct position within the main body of the vertebra has been reached, a bone compression device, which is nothing more than a balloon that is inflated by means of liquid or equivalent systems, is inserted by means of the cannula. The balloon performs the function of compacting the trabeculae of the cancellous bone of the main body of the vertebra, while at the same time expanding the internal cavity of the collapsed vertebra.
Once the cavity of the vertebra has been expanded by means of the balloon, the latter is retracted and cement of common use in orthopaedics, namely PMMA (polymethylmethacrylate), is inserted into the cavity thus formed, always by means of a cannula.
The use of cement in kyphoplasty has the advantage of immediately ensuring primary stability, namely resistance to the compression loads that act on the column, which guarantees a very short hospitalisation for the patient, such that the patient himself can be discharged within a few days of surgery.
On the other hand, many drawbacks are associated with the use of PMMA in kyphoplasty.
A very first drawback connected to the use of cement is the development of heat generated by the polymerization reaction, which is highly exothermic. The increase in temperature (12-14 Kcal are produced per 100 g cement) homogeneously develops within the concrete mass to then be transmitted towards the surface where it is disposed of. Temperatures close to 80° C. are also reached. Such high polymerization temperatures can cause localised bone necrosis problems.
A further disadvantage arising from the use of cement consists of the fact that microscopic cement fragments can become detached and escape from the main body of the vertebra through the fractured cortical bone fractured. Cases in which cement particles have escaped from the vertebra causing thrombi or other extremely dangerous situations for the patient are not rare in literature.
Not least, a problem left unresolved by the kyphoplasty surgeries of the type described thus far and which use cement to restore the support function performed by the cancellous bone having trabecular structure, consists of the fact that the surgery does not treat the compromised bone, in particular it does not treat the fracture, but limits itself to replacing the compromised cancellous bone with a synthetic material that accomplishes the support function performed by the healthy bone.